Method of reducing metal oxides



United States YPatent O "P METHOD oF REDUCING METAL oXIDEs Harry V.Rees, Chappaqua, and Frederick Burton Sellers, Tarrytown, N. Y.,assignors to Texaco Development Corporation, New York, N. Y., acorporation of Delaware Application February 15, 1955, Serial No.488,248

8 Claims. (Cl. 75-26) This invention relates to a process for thereduction of a metal oxide with a carbonaceous fuel and the simultaneousproduction of carbon monoxide and hydrogen. In one of its more specicaspects, this invention relates to a process for the simultaneousreduction of an iron oxide to metallic iron and the partial oxidation ofa liquid hydrocarbon to carbon monoxide and hydrogen. Hydrocarbon gas,oil, coke, and various coals including lignite, anthracite, andbituminous coals are suitable as fuels for the process of thisinvention.

In the process of the present invention, a reducible metal oxide inpowdered form is dispersed in an oxygen-containing gas and interactedWith oxygen and a carbonaceous fuel at a temperature above 2,000 F. Theparticles of solid reactants are dispersed in gaseous reactants andreaction products in the reaction zone. Reduction of the metal oxidereleases oxygen for oxidation of carbon from the fuel. Free ox gen isadded in an amount suiiicient to supply the necessary heat for thereaction with the simultaneous production of carbon monoxide. Thereduction product of the metal oxide, e. g., the metal, is removed fromthe generator, generally in molten form. Gaseous products of reactioncomprising carbon monoxide and hydrogen are also formed and may berecovered for fuel or as feed gas for chemical processes.

The present invention is particularly suited to the production of pigiron from iron ore and the simultaneous gasification of a liquidhydrocarbon by reaction with steam and oxygen to produce carbon monoxideand hydrogen. A flow-type gas generator of the type employed forproduction of synthesis gas from the fuel and an oxygen containing gasis used in the present process.' Such a generator is disclosed in thepatent to Du Bois Eastman and Leon P. Gaucher, 2,582,938.

The How-type generator is characterized by the reaction of a gaseousdispersion of fuel with oxygen in an unpacked and unobstructed reactionzone. It is important that the reaction zone be compact, presenting arelatively small 'amount of surface in comparison with its volume andthat it be designed to minimize heat losses by radiation. lt ispreferable to arrange the inlet and outlet of the reaction zone relativeto one another such that the reactants and reaction products flowsubstantially uniformly through the reaction zone, for example, as byintroducing the reactants at or near one end and withdrawing reactionproducts at or near the other.

The reaction zone preferably is generally cylindrical in shape with aninternal surface area not greater than about one and one-half times thesurface of a sphere of equal volume. Openings and black body surfacesare kept at a minimum to prevent loss of radiant heat from the reactionspace. Free transfer of heat by radiation is achieved in this typereaction vessel so that the entire reaction zone operates essentially ata single uniform temperature. The quantity offuel supplied to thegenerator is just sufiicient to react with oxygen and steam presenttherein so that the fuel is almost completely consumed.

2,824,792 Patented Feb. 25, V195,8

ICC

For most successful operation of a generator of this type for theproduction of carbon monoxide, the temperature throughout the generatormust be maintained within the range of from about 2,000 F. to about3,000 F., or higher. Practical considerations, especially apparatuslimitations, usually limit the maximum operating temperature to about2,600 F. At these temperatures, the slag from the fuel and metal oxide,if present, are molten and iluid.

In accordance with one embodiment of the present invention, a reduciblemetal oxide, e. g., iron oxide, is admixed with Water to form a slurry.The slurry is passed through a tubular heating zone as a continuousstream. The slurry is heated in the heating zone to a temperature atleast suliicient to vaporize the water. Vaporization of the water tosteam results in a great increase in volume which in turn greatlyincreases the velocity in ow of the stream. The solid particles aresuspended inthe stream of steam forming a dispersion and are subjectedto the disintegrating action of the highly turbulent ow of the confinedstream of steam. The dispersion of powdered solids is passed intoadmixture with oxygen and fuel in a owtype generator maintained at atemperature above about 2,000 F. All of the steam may be passed to thegenerator or part or all of the steam may be separated from thedispersion. Liquid hydrocarbon may replace all or part of the Water asthe slurrying medium.

Oxygen from the metal oxide enters into reaction with a portion of thecarbon from the fuel to produce carbon oxides. Additional oxygen issupplied in uncombined form in an oxygen-containing gas stream,preferably with a high concentration of free oxygen, to provide theamount necessary to maintain the reaction temperature. The total oxygensupplied to the reactor, as both free and available combined oxygen,relative to the carbon in thefuel may be expressed as the O/C ratioWhere O represents pound atoms of oxygen, and C, the pound atoms ofcarbon. Gen# erally, the total oxygen necessary to supply the heatrequirements of the process will be considerably in excess of the amounttheoretically required to convert all of the carbon to carbon monoxide.The total O/C ratios may vary from about 1.05 to about 2.0, dependingupon the relative amounts of fuel and metal oxide supplied to thegenerator.

Suitable metal oxides include the oxides of iron, copper, vanadium andbarium. The reduction product may be reconverted to the desired metaloxide or utilized as a product of the process. Barium peroxide, forexample, is readily converted to barium oxide and is easily reconfverted to the peroxide.

The reduction product of the metal oxide, i. e., either metal or a lowermetal oxide, may be removed from the generator either as solid particlesentrained in the product gases, or Withdrawn separately in molten form.With an iron oxide, or iron ore, as the metal oxide, it is preferable tooperate the generator at a temperature on the order of 2,500 F. orhigher and to draw off both iron and slag in molten form, as in blastfurnace operations.

The generator pressure may vary from atmospheric pressure to an elevatedpressure on the order of 500 .pounds per square inch gauge, or higher.

Limitations imposed by structural materials and the high temperaturesrequired, will determined the allowable operating pressure.

The quantity of liquid admixed with the solid to form a fluid slurry mayvary considerably. A minimum of about 35 percent liquid by volume isrequired, based upon the apparent volume of the granular solid. Theslurry may be readily pumped with suitable equipmentfor.exf ample, witha piston pump of the type commonly used. for handling drilling mud inoil well drilling operations.

The solid feed material need be reduced only to a particle size suchthat it may be readily handled as a suspension: or a slurry.V y Itgis,preferable toruse particles smaller Y thanuabout l@ inch in averagediameter; particles `of 1,00 mesh size.V and smaller are `more readilyhandled in a maybe prepared with acompositeimixture ofparticlessntfiallerthan MiY Yinch in` size, the b ulk of which comprisesparticles within the range of fromabout-Mi inch VtoVZOO mesh."y f' Y f.The slurry gatedl externally heated` tubular heating zone of restrictedcross-sectional area.V VThe heating may be eectively l' carried 4out'infa tubular helical coil or` pipe still type i 1 furnace, such as thefurnaces commonly used for, heating liquid streams in `the'refiningofpetroleum. The slurry Vis 'fed into the heated tubeat a rate suicient toprevent settling `out of the solid particles. The linear Vvelocity ofslurry-at the inlet to the heating tube should generallybe Within 'therange of from about 1/2 to l0 feet per second, suitably aboutl foot persecond. The velocity of, gaseous dispersion of powdered coal and Vapor,e. g., at the outlet of the tube, iswithin vthe range of from about 25to about Higher Yvelocities may be used.

Pressure, in itself, is notcritical in the heating step.

VThe `temperature and pressure.V relationships effecting vaporizationare well known. The pressure may be co- Vordinated with associatedprocesses.

Apotassium salt, preferably potassium carbonate, may

Y, be added Vto the slurry to increase therate of burning lof theVfuel'andri'luxingY of ash and slag in the generator.

' Arrportion "of, theV free oxygen, preferably.. a minor' amount, maybeadded tothe Vslurry charged to the heatslurry' and are preferred.lnrgeneral, a satisfactory slurry Y is heated by passing it through an,elon-4 2000 feet persecond, suitably about 300 feet per second.'

in'gr'zone.V Some reaction may take placebetween the oxygen'or metaloxide and the fuel in theheating zone. Tl'his reaction increases thetemperature in the heating zone andVV aids in the disintegration of thesolid materials.

A"flux may beused to reduce the fusion temperature ofthe'slagor torender it Vmore iluid. Lime is generally suitable as the flux, where oneis indicated, although itr may be vdesirable to add uorite, silica oraluminaV to increase the quantity or lluidity of theslag. YTheadditionofV lime to the generator not only increases Huidity of the slagand` decreases the uxing temperature but also effects removal of atleast a portion of the hydrogen sulfide from the product ,ga-s streamfrom feed materials containingrsulfur. Theamount of lime required asflux may be deter-V mined from the composition of the ironV oreV and4ash. In general/,the most satisfactory fusion is obtained when the sumof the lime and magnesia in the feed is approximately equalin weight tothe sum ofthe silica md alumina. Y The Y VVlirneand magnesia may beadded inthe formof the carbonates, but should be converted toVequivalent quantities of the oxides 1 n determining the quantityof uxrequired. Y Oxygen-enriched air orcommercially pure oxygen may Y be usedin the process. Commercially pure oxygen is preferred, Vespecially forthe generatio'nrof gases free.A from nitrogen, e.-- g.,hydrocarbonsynthesis feed gas. In the generation Vof gas for ammoniasynthesis,it maybe de- Vsirable to use oxygen-enrichedair.Y Y y The-invention will be fmore'readilyunderstood from 'the accompanyingdrawings and the following detailed description of preferred modes ofoperation ofthe process.

. .asa/avais:Y

liquid, e. g.,"fuel oil, may be supplied through line 7,

while .watermaybelsupphed Nthrough Aline ,8; Additive materials, e. g.,aflux, oxidation'catalyst, or an ernulsify'Y ing agent, may be added tothe mixer with'the metalV oxide, oil, or water., VVThe resulting slurryof'solid particlesV in liquid is passeduthrough line 10 to a pump 11from f which .itis passed through atuhular heaterV 1,2. Steam or gasmaybe introduced ,into the slurryfeedrstream ahead of the-heaterthrough'line 13 or into the heating coil 12V j The ,slurry is heated inheater 12 to a temperature at, least sufcient to vaporize the liquid.The resulting disper- Y sion of solid particles in vapor is dischargedinto a cyclone Y separator 17. Part or all of the vapor may be separatedfrom Vthe dispersionin the cyclone separator. Vapors areV i dischargedfrom the Vseparator V17 through line `18. The` solids are passed throughline 19 into a'ow-typegenerator Y 20. Oxygen is supplied to thegenerator through line 21.

`A gaseous product comprising mainly carbon monoxide fr Y and hydrogenis discharged from the generator through* line 23. The metal oxidereduction product, e. g., molten metal, is drawn'oi through line 25. VWhen Voil is used in theV preparation'of the slUlIY,"the

heater may befemployed to vaporize the oilwith minimum.Y

decomposition or cracking of the oil. On the other hand,

the oil'may be cracked to any desired extent bycontrolling Y theconditions in the heating'coil.` Y `If vaporization Without'cracking isdesired, it is V-ad vantageous thats'team be present in theheater-toreducc the partial pressure of the oiland aid inits'vaporization.

Steam maybe supplied from water contained in the slurryV Y andconvertedinto steam in the heater. Alternatively, or conjunctively, steam from anexternal source may be added to the slurry charged to the heating 'zoneor it'may be in! troduced into the heating zone at a point along thepathVof. flow through the heater. Gas, for example, hydrogen or aVgaseoushydrocarbon, maybe introduced'V into the stream `of slurry orinto the heating coil'in a similar,

manner.V Y

Y If` desired, the heater, maybe operated to crack the` oil 4so ,that`the stream discharged from the Yheater into the cyclone comprises theoil vapors, vincluding products -j of cracking, and themetal oxide (orits reduction products). The oil vapors may be Y.substantiallycompletely separated from'thesolid and processed for therecovel'yofrdesirable products. Y' Coke resulting fromrc'r'ackingpof theoi1villtllelieater may be deposited on theparticlesof metal oxide. Any cokepresenton'the metal Voxide parti- For convenience Vin the descriptionrofthe process, as illus- Y Vtrat'ed kin the,drawin'gs,.iron oxide isre-ferredto asfthe reducible metalroxide. It isY to be understood thatwhile iron oxide is taken as a preferred example for the purpose ofillustration, other metal oxides may be adrnixed with' or substitutedfor iron oxide. Y Y 1 Thegure is a'diagrammatic elevational view showinga suitable arrangement of Vapparatus for VAcarrying out a specificembodiment of the present invention.

Y'VWithpreferenceV to Vthe drawing, metal-oxide, e., g., crushedironore, is introduced throughlinezS into a mixer 6. Sufficient liquidto Vform a uid dispersion, for slutty,

is'admitted to the niixerethroiighline'or^throughliiieis or both.V .Asindicated in the drawing, a l1 ytlricaitbou Y' cles fed tothe gasgenerator helps reduce thewmetal Yoxide in the generator. Y s Y Themetal oxide may serve as a catalyst for the.con version ofthe..liydrocai'liorr A specific catalyst, vfor example, a crackingcatalyst,ga hydrogenationY catalyst,

or a hydrocracking catalystrmay be added to ,thevmetal oxide.` Asexamples vof suitable catalysts, silica, alumina, bauxite, magnesia,lime, and lacid-treated clays`,optionally containing oxidesor suldes ofmetals of Ygroups toY Ylll'oftheperiodic table',for example, .Y thefollowing.. metals, their oxides or sulfides: iron, molybdenum,co Y

balt, 'manganese vanadium, tungsten,` chromium, zinc, uranium, nickel,orrareearths. f When a metaLits oxide orqsultide, is=employed as ,aVcracking catalyst, itis generally desirable to choose as Vcatalyst ametal, orthe compound of a metal which is Vdesirablel in the reductionproduct of kthe major metal oxide,V reduced in the process.

mixture Yof oil and water, may" For example, vanadium, nickel, chromium,cobalt or molybdenum are often desirable in steel so that one or more ofthese metals or their compounds may advantageously be employed in thereduction of iron oxide. Alumina, silica, magnesia and lime are, aspreviously mentioned, fluxing agents which, in addition to catalyticproperties, may be useful for the removal of impurities from the ore byforming a slag which may be separated from the molten metal.

In a specific example of a mode of operation of the process of thisinvention, a mixture of oil and Water is used for the preparation of aslurry of metal oxide particles, for example iron oxide. The relativeproportions of oil and water are so chosen as to meet the fuel and steamrequirements of the generator. The slurry is passed through the heaterwherein the oil and water are completely vaporized forming a dispersionof metal oxide particles in vapor. The resulting dispersion is passeddirectly into the generator without any separation of vapor therefrom.Oxygen in the required amount is supplied to the generator intoadmixture with the steam, hydrocarbon vapors and solids. The oxygen,steam, hydrocarbon and metal oxide react in the generator to form carbonmonoxide and hydrogen with the simultaneous reduction of the metaloxide. The metal oxide reduction product, for example iron, is withdrawnfrom the generator in molten form.

Fuel may be supplied to the generator through line 22 as required foroperation of the generator. When fuel is supplied to the generatorthrough line 22, preferably the fuel is a hydrocarbon. Either liquid orgaseous hydrocarbons may be used. Most advantageously, when conversionof the hydrocarbon takes place in heating coil 12, at least the majorportion of the vapors is separated from the dispersion in separator 17and processed for recovery of desirable constituents. Undesirablehydrocarbons, e. g., gases and high carbon residuum, may be passedthrough line 22 as fuel for the generator. Other carbonaceous fuels, e.g., solid fuels including coke and coal, may be employed as fuel for thegenerator.

The following examples illustrate the application of the process to thereduction of iron ore to pig iron while at the same time producingcarbon monoxide and hydrogen in good yields.

Iron ore from the Mesabi Range containing 90 weight percent iron oxideand about 7.5 weight percent silica is mixed with heavy fuel oil to forma slurry. The oil has the following characteristics:

Limestone containing 97.3 weight percent calcium carbonate and 1.6percent magnesium carbonate is used as flux. The limestone is mixed withthe ore and oil to form the slurry. The slurry is pumped through aheating coil where it is heated to 800 F. The resulting preheated slurryis contacted with 800 F. steam in an atomizing nozzle in a flow-type gasgenerator Where it is atomized into admixture with oxygen of 99.5 volumepercent purity preheated to 295 F.

The generator is operated at about 2,800 F. and 220 pounds per squareinch gauge. For each ton of iron ore charged to the generator 203 poundsof limestone, 2,408 pounds of oil, 1,348 pounds of water and 30,223stand- 6 ard cubic feet of oxygen are required. For each ton of iron orecharged to the process 1,323 pounds pig iron and 139,784 standard cubicfeet of gas are produced. The pig iron produced in the process containsweight percent iron, about 3 weight percent carbon and about 1.5 percentsilica.

The gas produced in the process has the following composition on a wetbasis:

Mol percent The gas produced in the process may be purified and treatedto produce valuable by-product gas having a net heating value of about300 B. t. u. per cubic foot or a synthesis gas or hydrogen-rich stream.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made Without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. A process for the simultaneous reduction of a reducible solid metaloxide and the production of carbon monoxide and hydrogen which comprisesadmixing said metal oxide in solid particle form with su'icient liquidhydrocarbon to form a slurry; passing said slurry as a conned stream inturbulent ow through a tubular heating zone; heating said slurry to anelevated temperature at least sufficient to vaporize said liquidhydrocarbon; discharging the resulting dispersion comprising heatedsolid and hydrocarbon vapor into a reaction zone into admixture with gascontaining free oxygen; effecting interaction of said metal oxide,hydrocarbon and oxygen in the reaction zone at a temperature above about2,000 F. and recovering from the reaction zone the reduction product ofthe metal oxide and a gaseous product comprising carbon monoxide andhydrogen.

2. A process as dened in claim 1 wherein the ternperature within thereaction zone is above the melting point of the reduction product of themetal oxide.

3. A process as defined in claim l wherein steam is supplied to saidreaction zone as a reactant.

4. A process as defined in claim 1 wherein said solid metal oxide is anoxide of iron.

5. A process for the simultaneous reduction of a reducible solid metaloxideand the production of carbon monoxide and hydrogen which comprisesadmixing said metal oxide in particle form with a liquid hydrocarbon andwater to form a slurry; passing said slurry as a conlined stream inturbulent flow through a tubular heating zone wherein said liquidhydrocarbon and the water are vaporized; forming a dispersion comprisingsaid particles of metal oxide in vapor; introducing said dispersion intoa reaction zone into intimate admixture with gas comprising free oxygen;effecting interaction of said metal oxide, hydrocarbon, steam and oxygenin the reaction zone at a temperature above about 2,000 F.; andrecovering from the reaction zone the reduction product of the metaloxide and a gaseous produ-ct comprising carbon monoxide and hydrogen.

6. A process as defined in claim 5 wherein said metal oxide is an oxideof iron and said gas containing free oxygen is substantially pureoxygen.

7. A process according to claim 4 wherein limestone is supplied to thereaction zone as a ux and the reduction products comprises moltenmetallic iron.

Y Y f7 8.1.15 process according to claimV 5 `wherein said reaction -zonei s mavipignedt a speratmospheric pressure 91T thV gTdellf. 011200'[0'570'0 p. s, gr.V Y

r 'M Vlhei'egreerncersrCited in the 11eof this patent vUNITED STATESPATENTS 2,019,785` Janssen Nov. 5, 1935 Dill Ian. 12,V 1943 ,Y YHenminger Y Sept. 6, V1949 Ogdrz'aly etal.k JulyY 31, 1951 Y VLewis May12, 1953 McGrath et a1. Mar. 9,1954" Reeset al.y f Feb. V 15,1955

1. A PROCESS FOR THE SIMULTANEOUS REDUCTION OF A REDUCIBLE SOLID METALOXIDE AND THRE PRODCTION OF CARBON MONOXIDE AND HYDROGEN WHICH COMPRISESADMIXING SAID METAL OXIDE IN SOLID PARTICLE FROM WITH SUFFICIENT LIQUIDHYDROCARBON TO FORM A SLURRY; PASSING SAID SLURRY AS A CONFINED STREAMIN TURBULENT FLOW THROUGH A TUBULAR HEATING ZONE; HEATING SAID SLURRY TOAN ELEVATED TEMPERATURE AT LEAST SUFFICIENT TO VAPORIZE SAID LIQUIDHYDROCARBON DISCHARGING THE RESULTING DISPERSION COMPRISING HEATED SOLIDAND HYDROCARBON VAPOR INTO A REACTION ZONE INTO ADMIXTURE WITH GASCONTAINING FREE OXYGEN; EFFECTING INTERACTION OF SAID METAL OXIDE,HYDROCARBON AND OXYGEN IN THE REACTION ZONE AT A TEMPERATURE ABOVE ABOUT2,000* F. AND RECOVERING FROM THE REACTION ZONE THE REDUCTION PRODUCT OFTHE METAL OXIDE AND A GASEOUS PRODUCT COMPRISING CARVON MONOXIDE ANDHYDROGEN.